This application claims the benefits of Japanese Patent Applications P2001-219,092, filed on Jul. 19, 2001, and P2002-180,769, filed on Jun. 21, 2002, the entireties of which are incorporated by reference.
The invention relates to a method of producing a film of an yttria-alumina complex oxide, a film of an yttria-alumina complex oxide, a sprayed film, a corrosion-resistant member and a member effective for reducing particle generation.
In semiconductor manufacturing systems requiring a super clean state, halogen-based corrosive gases such as chlorine-based gases and fluorine-based gases are used as deposition gases, etching gases and cleaning gases. For example, these gases are used as cleaning gases for a semiconductor composed of a halogen-based corrosive gas such as CIF3, NF3, CF4, HF and HCl after the deposition stage in a semiconductor producing system, such as a hot CVD system. Further, halogen-based corrosive gases such as WF6, SiH2Cl2 or the like are used for film formation in the deposition stage.
Further, in film-forming and etching stages of CVD or PVD processes, the chemical reactions for film formation or etching produce by-products, which are deposited onto a susceptor, an electrode or the parts constituting the chamber. Particularly, in a so-called cold wall type system, the chamber wall is low in temperature, so that particles may be easily deposited onto the cold chamber wall. Although such deposits are subjected to wet or dry cleaning processes at predetermined intervals, excessive deposits may fall or be moved onto a semiconductor wafer, resulting in instability of semiconductor processing or reduction of the production yield.
To prevent falling particles, it has been known to apply shot peening or blast treatments using glass beads on the surface of a metal plate to increase the surface roughness, so that the retention force of the metal surface may be improved.
It has been thus desired to form a film that is highly resistive against halogen-based gases or plasmas and which is stable over a long time period on a member used for a semiconductor-producing system, such as a member contained in the chamber or the inner wall surface of the chamber. Further, when by-products are deposited on a member contained in the system or the inner wall surface of the chamber, it is desired that the deposited by-products are retained thereon for a long time period.
The assignee filed a Japanese patent application P2001-110,136. According to the disclosure, it is possible to form a film of an yttria-alumina complex oxide on a substrate by spraying and to provide a high anti-corrosion property against a halogen-based gas plasma, thus preventing the particle generation. The corrosion-resistant film, however, might leave the following problems. That is, cracks may be induced in the film depending on the conditions for spraying. The sprayed film may be subjected to a heat treatment at a high temperature. Such heat treatment may induce cracks in the film. If cracks are generated in the film of an article having a substrate and the film, such film may be easily peeled from the substrate to generate particles and reduce the anti-corrosion property against a corrosive substance. The resulting article may be undesirable, thus reducing the production yield.
An object of the present invention is to provide a film of an yttria-alumina complex oxide having a high peel strength on a substrate.
Another object of the invention is to provide a member effective for reducing particle generation and having a high capability for retaining deposits and that is usable for a long time period with improved stability.
Still another object of the invention is to provide a member effective for reducing particle generation and having a high capability for retaining deposits on the surface, so as to reduce the number of fallen particles due to the deposits on the member and reduce the down time associated with maintenance of a system applying the member.
A first aspect of the invention provides a method of producing a film of an yttria-alumina complex oxide, the method comprising the step of spraying a mixed powder of powdery materials of yttria and alumina onto a substrate to produce a sprayed film composed of an yttria-alumina complex oxide.
Further, the invention provides a film of an yttria-alumina complex oxide obtained by the above method.
Further, the invention provides a film of an yttria-alumina complex oxide, wherein the yttria-alumina complex oxide comprises those of garnet and perovskite phases and a ratio YAL(420)/YAG(420) is not lower than 0.05 and not higher than 1.5, provided that the ratio YAL(420)/YAG(420) is the ratio of a peak strength YAL (420) of the (420) plane of the perovskite phase to a peak strength YAG (420) of the (420) plane of the garnet phase. The peak strengths are measured by X-ray diffraction method.
Further, the invention provides a film formed by spraying, the film being made of an yttria-alumina complex oxide and free from a crack having a length not smaller than 3 xcexcm and a width not smaller than 0.1 xcexcm.
Further, the invention provides a corrosion-resistant member comprising a substrate and a film of an yttria-alumina complex oxide, wherein the yttria-alumina complex oxide comprises those of garnet and perovskite phases and a ratio YAL(420)/YAG(420) is not lower than 0.05 and not higher than 1.5, provided that the ratio YAL(420)/YAG(420) is the ratio of a peak strength YAL (420) of the (420) plane of the perovskite phase to a peak strength YAG (420) of the (420) plane of the garnet phase. The peak strengths are measured by X-ray diffraction method.
The invention further provides a corrosion-resistant member comprising a substrate and a film formed by spraying. The film is made of an yttria-alumina complex oxide and free from a crack having a length not smaller than 3 xcexcm and a width not smaller than 0.1 xcexcm.
Further, a second aspect of the invention provides a member effective for reducing particle generation and comprising a substrate and a surface layer on the substrate. The surface layer has a, calculated according to the following formula, in a range of 50 to 700:
xcex1=(a specific surface area measured by Krypton adsorption method (cm2/g))xc3x97(a thickness of the surface layer (cm))xc3x97(a bulk density of the surface layer (g/cm3)).
The inventors conceived of spraying a mixed powder of powdery materials of yttria and alumina on a substrate to form a sprayed film of an yttria-alumina complex oxide, and tried the process. Consequently, they have successfully formed a film having a high peel strength on a substrate with improved stability.
The thus obtained film of an yttria-alumina complex oxide does not have substantial cracks and has a high peel strength with respect to the underlying substrate, thereby preventing the peeling of the film and particle generation in contact with a corrosive substance. Additionally, when such a film is subjected to heat treatment, the peel strength of the film with respect to the substrate may be further improved, and cracks not observed in the film after the heat treatment.
Moreover, it is possible to control or regulate the microstructure of the film by controlling the conditions for the spraying process and for the heat treatment. Specifically, a porous film substantially without closed pores, or a porous film having a high ratio of open pores to closed pores may be successfully produced. A member for a semiconductor-producing system may be advantageously produced using such a film and the underlying substrate. Such a member has an improved specific surface area, so that deposits may be firmly held on the surface of the member by an anchor effect to reduce the thickness of the deposits on the member. It is thus possible to produce a film having a specific a value according to the invention of the second aspect, which will be described later in detail.
In a preferred embodiment, the powdery material of yttria has a 50 percent mean particle diameter in a range of 0.1 xcexcm to 100 xcexcm, to further reduce the crack formation and improve the anti-corrosion property against a corrosive substance such as a halogen-based gas.
The powdery material of yttria may preferably has a 50 percent mean particle diameter of not smaller than 0.5 xcexcm, and more preferably not smaller than 3 xcexcm, to further improve the adhesive strength of a film to a substrate. The 50 percent mean particle diameter of the powdery material of yttria is preferably not larger than 80 xcexcm, more preferably not larger than 50 xcexcm and most preferably not larger than 10 xcexcm, to further improve the adhesive strength of the film to the substrate.
In a preferred embodiment, the powdery material of alumina preferably has a 50 percent particle diameter in a range of 0.1 xcexcm to 100 xcexcm. It is thus possible to further reduce the crack formation and to further improve the anti-corrosion property of the film against a corrosive substance such as a halogen based gas.
The 50 percent particle diameter of the powdery material of alumina is preferably not smaller than 0.3 xcexcm and more preferably not smaller than 3 xcexcm, to further improve the adhesive strength of the film to the substrate. The 50 percent mean particle diameter of the powdery material of alumina is preferably not larger than 80 xcexcm, more preferably not larger than 50 xcexcm and most preferably not larger than 10 xcexcm, to further improve the adhesive strength of the film to the substrate.
The 50 percent mean particle diameter (D50) is calculated based on the diameters of primary particles when secondary particles are not observed, and the diameters of secondary particles when the secondary particles are observed, in both of the powdery materials of yttria and alumina.
The mixed ratio of the powdery materials of yttria and alumina is not particularly limited. The ratio (yttria/alumina), however, is preferably 0.2 to 1, and more preferably 0.5 to 0.7, calculated based on the molar ratio of yttria and alumina molecules.
The mixed powder may contain a powdery material of a third component other than yttria powder and alumina powder. It is, however, preferred that the third component does not adversely affect the crystalline phases, such as garnet and perovskite phases, of the yttria-alumina complex oxide, which will be described later. More preferably, the third component is a component capable of replacing the sites of yttria or alumina in the garnet or perovskite phases of an yttria-alumina complex oxide. The third component may preferably be selected from the following: La2O3, Pr2O3, Nd2O3, Sm2O3, EU2O3, Gd2O3, Tb2O3, Yb2O3, La2O3, MgO, CaO, SrO, ZrO2, CeO2, SiO2, Fe2O3 and B2O3.
When spraying the mixed powder, the mixed powder may be sprayed on a substrate without substantially adding an additive. Alternatively, a binder and a solvent may be added to the mixed powder to produce granules by means of spray drying, and the granules may then be sprayed.
The mixed powder may preferably be sprayed under a low pressure. The pressure is preferably not higher than 100 Torr, to further reduce the pores in the sprayed film and to enhance the corrosion resistance of the resultant film.
In a preferred embodiment, the sprayed film is subjected to a heat treatment, to further improve the peel strength of the film with respect to the substrate.
The film is preferably heat treated at a temperature not lower than 1300xc2x0 C., and more preferably not lower than 1400xc2x0 C. It is considered that a layer of a reaction product may be formed along the interface between the substrate and film by increasing the heat treatment temperature to at least 1300xc2x0 C., so that the peel strength may be improved.
The temperature for the heat treatment has no particular upper limit, so long as the substrate is not degraded or decomposed. The temperature for the heat treatment is preferably not higher than 2000xc2x0 C., to prevent the degradation of the substrate. When the temperature for the heat treatment of the sprayed film approaches 1800xc2x0 C., aluminum elements may move and diffuse around the layer of a reaction product once formed along the interface between the film and substrate. Such movement may inversely reduce the peel strength of the corrosion-resistant film. From this point of view, the temperature for the heat treatment is preferably not higher than 1800xc2x0 C. Further, the temperature is preferably not higher than 1700xc2x0 C. to prevent crack formation in the film.
This film may be formed continuously over the surface of the substrate. The film, however, may also be formed non-continuously over the entirety of a predetermined face of the substrate. For example, the film may be formed discontinuously on the surface of the substrate. The film may also be formed as a plurality of layer-like islands. In this case, such layer-like islands are not continuous with one another. Alternatively, the film may exist in a dotted manner or in a scattered arrangement on a predetermined surface of the substrate.
In a preferred embodiment, the inventive film is substantially free from cracks. Particularly, the inventive film is free from cracks having a length of not smaller than 3 xcexcm and not smaller than 0.1 xcexcm. The presence of such microcracks may be detected by observing a film using a scanning electron microscope applying a magnification of at least 1000xc3x97.
The material of a substrate is not particularly limited. Preferably, the material does not contain elements which might adversely affect the process carried out in a container for plasma generation. From this point of view, the material of a substrate may preferably be aluminum, aluminum nitride, aluminum oxide, a compound of aluminum oxide and yttrium oxide, a solid solution of aluminum oxide and yttrium oxide, zirconium oxide, a compound of zirconium oxide and yttrium oxide, and a""solid solution of zirconium oxide and yttrium oxide.
The peel strength of the corrosion-resistant film with respect to the substrate is measured by Sebastians test, assuming that the diameter of the bonded face is 5.2 mm.
The substrate may be porous. The center line average surface roughness Ra of the surface of the substrate is not smaller than 1 xcexcm and more preferably is not smaller than 1.2 xcexcm. It is thus possible to improve the adhesive strength of the film to the underlying substrate and to reduce the particle generation due to the peeling of the film.
The kind of yttria-alumina complex oxide is not particularly limited, and may be selected from the following:
(1) Y3AL5O12 (YAG: 3Y2O3.5Al2O3) This oxide contains yttria and alumina in a molar ratio of 3:5 and has garnet crystalline phase;
(2) YAlO3 (YAL: Y2O3Al2O3) perovskite crystalline phase; and
(3) Y4Al2O9 (YAM: 2Y2O3.Al2O3) monoclinic system.
In a preferred embodiment, the yttria-alumina complex oxide contains at least a garnet phase. Further in a preferred embodiment, the yttria-alumina complex oxide contains garnet and perovskite phases. It is thereby possible to further improve the peel strength of the film with respect to the substrate and to reduce crack formation.
Particularly preferably, the yttria-alumina complex oxide contains garnet and perovskite phases. A ratio YAL(420)/YAG(420) is not lower than 0.05 and not higher than 1.5. The ratio YAL(420)/YAG(420) is the ratio of a peak strength YAL (420) of the (420) plane of the perovskite phase to a peak strength YAG (420) of the (420) plane of the garnet phase. The peak strengths are measured by X-ray diffraction method.
YAL(420)/YAG(420) is preferably not lower than 0.05, or not higher than 0.5.
The inventive film, or laminate of the film and a substrate, has a superior anti-corrosion property, especially against a halogen-based gas or a plasma of a halogen-based gas.
The corrosion resistant member according to the invention may be used for a system of producing semiconductors such as thermal CVD system to make use of its anti-corrosion property. In a system for producing semiconductors, a semiconductor cleaning gas of a halogen-based corrosive gas is used. The corrosion resistant member according to the invention is corrosion resistant against a plasma of a halogen-based gas, as well as a plasma of a mixed gas of a halogen gas and oxygen gas.
Such halogen gases include ClF3, NF3, CF4, WF6, Cl2, BCl3 or the like.
The second aspect of the invention provides a member effective for reducing particle generation comprising a substrate and a surface layer on the substrate. The layer has a specific surface area per unit area xe2x80x9cxcex1xe2x80x9d of not lower than 50 and not higher than 700.
When generated by-products and particles deposit on the surface of the member, the deposited by-products and particles may be held in pores of the surface layer, thus preventing the falling or dispersing of the by-products and particles from the surface layer. It is thus possible to reduce semiconductor defects that result from the falling and dispersing of the particles and thereby to reduce the down time of the entire system required for cleaning the deposits on the member.
The specific surface area per unit area xe2x80x9cxcex1xe2x80x9d is defined according to the following formula:
xcex1=(a specific surface area measured by Krypton adsorption method (cm2/g))xc3x97(a thickness of the surface layer (cm))xc3x97(a bulk density of the surface layer (g/cm3)).
As can be seen from the above formula, xe2x80x9cxcex1xe2x80x9d is a kind of index indicating a specific area per unit surface area of a surface layer. The surface area of the surface layer may be calculated, for example, from a design drawing. More specifically, the surface area is calculated on the assumption that the surface is smooth without any irregularities formed on the surface of the layer.
The specific surface area measured by Krypton adsorption method (cm2/g) refers to a specific surface area (cm2) per unit weight (g). That is, the specific surface area refers to the adsorption capacity per unit weight of the surface layer. In other words, that means the amount and diameters of open pores effective for adsorption per unit weight of the surface layer.
On the other hand, the thickness (cm) of the surface layer is multiplied by the bulk density of the surface layer (g/cm3) to obtain a weight per unit surface area of the layer (g/cm2). The weight per unit surface area of the layer (g/cm2) is then multiplied by the specific surface area measured by Krypton adsorption method (cm2/g) to obtain a specific surface area per unit surface area (cm2/cm2), which is xe2x80x9cxcex1xe2x80x9d. Therefore, xe2x80x9cxcex1xe2x80x9d is an index indicating the adsorption capacity of a gas, or the amount and diameters of open pores, per unit surface area (1 cm2) of the surface layer. The bulk density is the density calculated by dividing the weight by volume containing open pores and closed pores.
The xe2x80x9cxcex1xe2x80x9d value has to be controlled to a value not lower than 50 in the present invention. A surface layer having such large specific surface area per unit area xe2x80x9cxcex1xe2x80x9d is provided on a substrate, according to the present invention, so that the by-products and particles may thereby be adsorbed, adhered or held in the open pores in the surface layer. It is thereby possible to reduce the falling or dispersion of particles from the surface layer. From this point of view, xe2x80x9cxcex1xe2x80x9d may preferably be not larger than 100.
When xe2x80x9cxcex1xe2x80x9d is small, the surface area for holding and adsorbing the by-products is insufficient, so that the by-products deposit on the surface layer to form a thicker deposits to increase the deposits fallen from the surface layer, even when the amount of the generated by-product is not increased. Such thicker deposits increase the by-products fallen from the surface layer. Additionally, the surface area exhibits a relatively poor anchor effect, so that the holding capacity of the by-products in the surface layer is reduced.
Besides, even xe2x80x9cxcex1xe2x80x9d of at least 50 is apparently larger than that of conventional members produced by blasting well known in a shield plate or the like used for a sputtering system (see comparative examples C1, and C2: tables 3 and 4).
When the specific surface area per unit area xe2x80x9cxcex1xe2x80x9d of the surface layer is made large, the surface area for adsorbing the by-products and particles is also increased. It is therefore speculated that the increased xe2x80x9cxcex1xe2x80x9d is advantageous for preventing the falling and dispersion of the particles and by-products. Contrary to the speculation, however, it was found that when xe2x80x9cxcex1xe2x80x9d exceeds 700, the amount of fallen and dispersed particles is increased. The results may be explained as follows. If xe2x80x9cxcex1xe2x80x9d is beyond 700, the ceramic bone structure constituting the surface layer is fractured microscopically when thermal cycles are applied. Such fractures may contribute to the increase of the particles. From this point of view, xe2x80x9cxcex1xe2x80x9d is preferably not larger than 500, and more preferably not larger than 300.
The effects, features and advantages of the invention will be appreciated upon reading the following description of the invention when taken in conjunction with the attached drawings, with the understanding that some modifications, variations and changes of the same could be made by the skilled person in the art.